One design could be ovular, resting on 4 or 5 pilings (each about 12’ high—to near middle of house height) that act as base isolators to withstand earthquake shaking. Stairs will lead up to the front door. The house is attached to a cable that comes up to the middle of the underside of the house or attached to a utility pole to keep it grounded, so it can float up and down in case of flood. Its aerodynamic styling allows it to rotate so that debris floating down a river will float around it, while the cable holds it in place, so that it can easily be reset. In hurricanes, the wind can blow around, under and over it. It might also rotate in a tornado, while the cable holds it in place (perhaps from a Safe Room). If not, it can be airborne in a tornado, but remain intact with its hardened shell. One architect’s alternative suggestion would be to attach two rings to the house on opposite sides each embracing a piling that would allow a more stabilized vertical-only movement.
Materials will be lightweight, heat/cold resistant, and dent/crack-proof, so that hail, ice/freeze, heat/fire won’t bother it. It can be made of about 6-8 pieces that can be easily snapped together, and have some kind of pull-down shuttering or pop-in coverings to protect the windows. It’d be hooked up to sewage and water like a mobile home.
There will be enough room inside to have a large common room (living room and dining room combo) with a small kitchen facility off to the side, 2-3 small bedrooms, and a bath.
The total cost should be about $10K--$15K when it’s mass-produced, esp. if made from compressed agricultural by-products that are made into panels for easy shipping. It’d be for temporary (or permanent) housing for victims whose homes are destroyed by the likes of Hurricane Mitch or Katrina. Of course, there will be a small, additional cost for transportation, set-up, plumbing, and electrical work.
Any architects willing to design this?

May 30 2011:
I think the Hexayurt (http://en.wikipedia.org/wiki/Hexayurt) achieves quite a few of your design goals. As for some of the others - it intuitively feels like the kind of flood or hurricane you're trying to avoid will take any cables/poles/floats with it. Especially when you're imagining having plumbing/rooms/stairs etc. I think your 4-6 hour requirement (sensibly) implies that packing up and moving, even temporarily, is a better solution than trying to beat many different types of disasters.

Anyway, the hexayurt should give some great ideas to solve many of the challenges you have proposed.